Engines may utilize various adjustments during cold start operation to rapidly increase temperature of an exhaust catalytic emission control device. Specifically, spark retard may be used to increase exhaust gas temperature, thereby enabling the device to reach a light-off temperature in a shorter duration, thus reducing cold start emissions. As another example, the combustion air-fuel ratio may be set slightly lean to further increase exhaust temperature and reduce exhaust hydrocarbon emissions.
However, the inventors herein have recognized various issues with such adjustments. For example, excessive spark retard can increase susceptibility to combustion instability at low temperature, or due to disparate fuel qualities. Likewise, enleanment at cold starting conditions may also lead to engine misfires and/or combustion instability.
As such, in one approach, a method is provided for operating an engine having an intake, an exhaust, and a hydrocarbon-retaining system, the engine combusting fuel, the method comprising: during engine starting: selectively routing exhaust gases of the engine to the hydrocarbon retaining system to store exhaust hydrocarbons and operating with spark advance close to a peak torque timing; and selectively purging stored hydrocarbons from the hydrocarbon retaining system to the engine intake.
In this way, it is possible to reduce reliance on spark retard, since the hydrocarbon retaining system addresses cold start emissions. Thus, even assuming the light-off time for the catalyst increases, emission may still be reduced. Thus, it is possible to increase combustion stability while reducing exhaust emissions.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.